Structural, Electrical Properties and Magnetoresistive Effect in the (La1-xDyx)0.67Sr0.33MnO3 Compound

Abstract:

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The significant influences of substituting low concentration Dy at La- site for
La0.667Sr0.333MnO3 perovskites compounds in structural, electrical and magnetoresistance properties
have been studied. The polycrystalline samples (La1-xDyx)0.667Sr0.333MnO3 with x= 0.00, 0.02 and
0.10 were synthesized via conventional solid-state reaction in bulk. This work measured their
resistivity properties with (below 1 Tesla) and without the presence of magnetic field (0 Tesla) as a
function of temperature, microstructure and particle distribution and structural distortion using four
point probe resistivity technique, X- ray diffractometer (XRD) and Atomic Force Microscope
(AFM). The resistivity in applied magnetic field or so-called magnetoresistance ratio is defined as
MR% = (Ro – RH)/RH x 100 was measured at 90K, 100K, 150K, 200K, 250K, 270K and 300K.
The highest MR% values for x=0.00, 0.02 and 0.10 are 15.3%, 15.5% and 20.6% at 1 Tesla
respectively. The metal- insulator transition temperature, TMIT correspond to >300K, 298K and
230K of sample with x= 0.00, 0.02 and 0.10 respectively were observed from resistivitytemperature
(R-T) curve.

Abstract: Polycrystalline samples of La0.67Ba0.33(Mn1-xRux)O3 with x = 0, 0.05, 0.1, 0.15 and 0.2
have been prepared using solid state reaction. The effects of doping of Ru at Mn site on La-Ba-Mn-
O ceramics, the characteristics and magnetotransport properties of CMR materials are investigated.
The magnetoresistance (MR) effect is measured using the four point probe technique. The
magnetoresistance defined as MR% = (Ro – RH)/RH x 100% was measured at a magnetic field of H
≤ 1T at 90K, 100K, 150K, 200K, 250K, 270K and 300K for the sample of doping x = 0, 0.05, 0.1,
0.15 and 0.2. Overall, MR drops slowly when temperature rises. All doping concentration gives
small variation range (~2.7% to ~26.78%). The electrical property has determined by using
standard four-point probe resistivity measurement in a temperature range of 30 K to 300 K. Metalinsulator
transition temperature (Tp) shifted to lower temperatures as Ru doping is increased. In this
paper the structural pattern and microstructure property have investigated via XRD. XRD patterns
show that these systems are in orthorhombic distorted perovskite structures.

Abstract: We have reported in this paper, the effect of grain size in Nd0.6Sr0.4MnO3 .We have investigated the effect of grain size on metal-insulator transition and Curie temperature. We have also reported here the variation of low field magnetoresistance with temperature and grain size. We have observed that the Curie temperature increases monotonically with particle size. The metal insulator transition temperature initially increases with particle size and then gets fixed to a certain value. In these Nd0.6Sr0.4MnO3 nanometric systems, any significant variation of magnetoresistance with particle size is not observed.

Abstract: The La0.8SrxCa0.2-xMnO3 (x=0, 0.05 and 0.15) compounds were synthesized by combining sol-gel method and high temperature sintering. The effects of Sr doping content on the microstructure, metal-insulator transition and magnetoresistance (MR) of the La0.8SrxCa0.2-xMnO3 were investigated. The results show that the La0.8SrxCa0.2-xMnO3 exhibit single perovskite phase and the change of Sr doping content can result in phase structure transition. The La0.8Sr0.15Ca0.05MnO3 is rhombohedra structure and the La0.8SrxCa0.2-xMnO3 shows distorted cubic structure when x is no more than 0.05. Increasing Sr doping content causes the degeneration of microstructure homogeneity and density and the decrease of average grain size of the La0.8SrxCa0.2-xMnO3, which can be attributed to the weakening of atomic diffusion during the sintering process. The metal-insulator transition temperature (TMI) of the compounds increases with the decrease of Sr doping content due to the improvement of microstructure. The La0.8Sr0.15Ca0.05MnO3 has the highest MR peak value, which is about 95%. The La0.8Ca0.2MnO3 has the highest room temperature MR, which is about 28%. Moreover, the magnetoresistance of the La0.8Ca0.2MnO3 is very stable between 125~300K.